Current trends in offshore oil and gas procurement indicate that the drilling and working of underwater mineral deposits will be increasingly important in providing the world's oil requirements. Sites for the production of underwater mineral deposits are being found at locations further and further from shore. The submerged wells in offshore waters are often times at such great distances from shore that it is not feasible to transport the crude oil directly from the well site to onshore processing facilities by a pipeline. In such situations, accumulated oil is stored at the well site. Often, the storage of oil at the well site is accomplished by utilizing a submerged storage tank, moored in the bottom of the body of water. It becomes necessary to transfer the stored crude oil from a location under the surface of the water to a tank ship for transporting the crude oil to onshore processing facilities. It is desirable to have a device for ship mooring and fluid transfer between tank storage and tank ship.
Requirements for large quantities of crude oil at the lowest possible price has brought about changes in the manner of transporting oil between continents. In prevalent use for the transporting of oil are large supertankers. Supertankers due to their large size and deep draft are not able to dock at many ports. Those deep harbor ports are very crowded, and tankers often must wait long periods of time before loading or unloading its fluid cargo. To alleviate the problems associated with supertanker transporting of fluid cargo, it is necessary for the supertankers to station themselves some distance from shore to receive or deliver cargo via underwater pipelines. To enable the supertankers to load and unload at these offshore positions, devices are required which moor the ship and provide the coupling link between the supertanker and the underwater pipeline.
Problems have been encountered in prior art offshore terminals where it is anchored and held rigid permitting very little movement of the terminal in response to wind, waves and currents. In addition for most offshore terminals, flexible hose are utilized to connect the underwater pipeline outlet with the fluid conduit connectors at the terminal. As a result, any twisting movement of the offshore terminal will place great stress on the hoses requiring replacement by procedures which are both time consuming and expensive.
Additional problems encountered with prior offshore terminals have concerned the flow line from the underwater pipeline to the surface of the water. Being very long, it is subjected to considerable force from undersea currents. In addition, drifting of the tanker will change the position of the tanker in respect to the flow line connecting to the tanker. Such a change in tanker position is reflected in a change in the required length of connecting flow line. Extreme changes of position of this sort put great stress on the connecting flow line which could possibly cause a rupture of the line. Excessive slack to allow for movement may allow the tanker to overrun and damage the hose.
Further, it is very necessary that the moored tanker be able to rotate about the terminal. A tanker when empty must be able to align itself into the wind and when loaded must be able to head into the current. In any other attitude, the moored tanker is unstable, and a danger of collision between the tanker and terminal exists.
There is accordingly provided by this invention a novel offshore marine terminal, for mooring tankers and transferring fluids between a tanker and an underwater pipeline, which includes a bathyal service chamber for creating an underwater work habitat at the mooring site which, when the terminal is lowered over an underwater manifold, can be used to make original anchor hookups and any subsequent repairs.
There is provided an offshore marine terminal which is suitable for deep, rough water locations and which has reduced surface buoyancy and short anchor lines.
There is further provided by the instant offshore marine terminal a configuration which reduces surface slack in the floating connection hose thereby preventing damage to the hose from overrun as the tanker moves about the mooring point.
There is also provided in accordance with this invention an offshore marine terminal which is easily maintained and permits repair or replacement of parts to be done more quickly.
There is yet further provided an offshore marine terminal in which the structure readily complies with tanker movement due to wind, waves and currents without developing high stresses on the mooring terminals or fluid connection hoses.
The novel offshore marine terminal in accordance with this invention has a buoyant member which floats in a body of water. A first end extends above the surface of the water, and a second end is submerged and extends beneath the water. A bathyal service chamber is on the second end of the member. The bathyal service chamber defines an underwater habitat which is suitable for maintaining humans in an artificial atmosphere. The terminal includes means to selectively change the buoyancy of the member allowing it to move from the first lowered condition to a second elevated position.
The member, when in the lowered position, has the bathyal service chamber positioned around an undersea manifold, pipeline, storage facility or the like. When the member is in the elevated position, the bathyal service chamber is disposed above the undersea manifold.
Flow lines to transport fluid between the manifold and the vessel extend through the bathyal service chamber. Also, short anchor lines secured to anchors can be used to secure the buoyant member to the subsea floor. The anchor lines would attach to the buoyant member at a position which would permit lateral movement of the first end of the member in response to movement of the surface vessel.
It is to be understood that, as used herein, the term "fluid" is intended to mean any liquid, gas or fluid slurry with solid particles suspended therein.